b7100 rebuild won't run

[snowklaw]

One of the crank bearings on my tractor spun so I rebuilt the bottom of the d750 on my B7100; new crank bearings, pistons and rings. The crank journals all got machined. The block was tested and the cylinders were bore out to accommodate the over-sized pistons.

On start-up it would blow all kinds of smoke, sputter for 5-10 seconds and die. It also sounded like it was knocking. I thought it just needed to break-in so kept at it checking everything I could think of; bad fuel, valve clearance, filters fuel pressure. (FYI - my first rebuild project ever). On a few tries I could get it to run longer but it sounded horrible and lacked power.

I pulled the head back off and found that two pistons had been hitting the intake valves. The heating element on the middle glow plug was also broken. I pulled the front cover and made sure all the timing markings matched up, then tested the compression; dry and cold I got 240, 200 and 245.

I'm inclined to think I need a new head. I'm about $1300 into the rebuild and I bought the tractor for $5500. I just can't keep throwing money at it but I want to prove to myself that I can fix it. If I knew it would run I would buy the head and replace the pistons and rings again.

Where did I go wrong?

 

[ASTER]

One of the crank bearings on my tractor spun so I rebuilt the bottom of the d750 on my B7100; new crank bearings, pistons and rings. The crank journals all got machined. The block was tested and the cylinders were bore out to accommodate the over-sized pistons.

On start-up it would blow all kinds of smoke, sputter for 5-10 seconds and die. It also sounded like it was knocking. I thought it just needed to break-in so kept at it checking everything I could think of; bad fuel, valve clearance, filters fuel pressure. (FYI - my first rebuild project ever). On a few tries I could get it to run longer but it sounded horrible and lacked power.

I pulled the head back off and found that two pistons had been hitting the intake valves. The heating element on the middle glow plug was also broken. I pulled the front cover and made sure all the timing markings matched up, then tested the compression; dry and cold I got 240, 200 and 245.

I'm inclined to think I need a new head. I'm about $1300 into the rebuild and I bought the tractor for $5500. I just can't keep throwing money at it but I want to prove to myself that I can fix it. If I knew it would run I would buy the head and replace the pistons and rings again.

Where did I go wrong?

we all get like this with every tractor, dump money in... an stuff like this happens... your psi is very low, like im shocked its running... also it sound like you have a timing problems... it almost sound like it a center gear prob

 

[snowklaw]

Thanks Aster for the prompt response. I reset my center gear so that all the timing marks matched up yesterday... I thought "this is it, this will do the trick..." It's exactly the same as before.

 

[SidecarFlip]

With the head off, I'd be measuring the piston protrusion as it relates to the deck height. Sounds to me like you have either the incorrect pistons, or the deck was milled past the acceptable limit and the protrusion is too much. You can compensate with a thicker head gasket but you must determine the protrusion first.

You'll need the shop manual, it will call out the acceptable protrusion in thousands of an inch (or mm). The you need a dial indicator and base and set it to deck height and then retract the indicator stem and slide it over the piston (edge not the center) and check the protrusion limit. I bet the pistons are sticking out too far at TDC. The you can determine how thick a head gasket you require to being it to spec.

Thicker than stock head gaskets will also require an adjustment in valve clearance settings because the engine don't have hydraulically actuated lifters so that thicker dimension has to be added to the valve clearance dimension when adjusting the set valve clearance.

Sounds complex but in reality, it's not.

 

[SidecarFlip]

Might add, did you check the deck for flatness with a straight edge? That is also listed in the shop manual. Use a straight edge and feeler gauge to determine flatness and check in various positions. Same applies to the head itself if you had the milled.

 

[snowklaw]

SidecarFlip thanks for the new ideas! Both are things I have not checked nor would I have known to do so. I'm going to pull the head the first chance I get. On assembly, I did notice that the pistons cleared the deck but I assumed that was normal to void the additional space created by the gasket.

The tractor had 30+ years of life experience before I got it, so who knows what else has been done to the engine.

 

[North Idaho Wolfman]

Hate to tell you this... But it's most likely junk now, and I'm not saying that to be mean.

That a sleeved engine, and if it was bored into the old sleeves it's junk!

A piston hitting a valve means either the valve were completely mal adjusted or the timing gears are off or they are the wrong pistons or they were installed backwards, yes they are directional pistons.

 

[whitetiger]

One of the crank bearings on my tractor spun so I rebuilt the bottom of the d750 on my B7100; new crank bearings, pistons and rings. The crank journals all got machined. The block was tested and the cylinders were bore out to accommodate the over-sized pistons.

On start-up it would blow all kinds of smoke, sputter for 5-10 seconds and die. It also sounded like it was knocking. I thought it just needed to break-in so kept at it checking everything I could think of; bad fuel, valve clearance, filters fuel pressure. (FYI - my first rebuild project ever). On a few tries I could get it to run longer but it sounded horrible and lacked power.

I pulled the head back off and found that two pistons had been hitting the intake valves. The heating element on the middle glow plug was also broken. I pulled the front cover and made sure all the timing markings matched up, then tested the compression; dry and cold I got 240, 200 and 245.

I'm inclined to think I need a new head. I'm about $1300 into the rebuild and I bought the tractor for $5500. I just can't keep throwing money at it but I want to prove to myself that I can fix it. If I knew it would run I would buy the head and replace the pistons and rings again.

Where did I go wrong?

Do you have a Work Shop Manual for this tractor?

 

[snowklaw]

Hate to tell you this... But it's most likely junk now, and I'm not saying that to be mean.

That a sleeved engine, and if it was bored into the old sleeves it's junk!

A piston hitting a valve means either the valve were completely mal adjusted or the timing gears are off or they are the wrong pistons or they were installed backwards, yes they are directional pistons.

Thanks Wolfman, I don't see it as mean... I appreciate the feedback. Interesting about the directional pistons. I did not know that. The machine shop advised me to bore out the cylinders... Being new to all this, I just went with it.

The two pistons that are hitting the valves are turned the opposite direction from the one piston that isn't hitting the valves (judging by the logo stamped on the face of the piston). I didn't notice that until I had everything apart the second time. And I didn't think anything of it because I assumed it didn't matter.

I bought the oversized pistons from Kumar Bros. The website indicated that they were the right ones. I also purchased the shop manual... that was after everything came back from the machine shop.

Well, it might be junk but I have a couple more ideas to check out. 1.) I'm going to turn the pistons around and 2.) check the clearance on the deck. 3.) read the shop manual from cover to cover... Thanks everyone for the help.

 

[snowklaw]

That a sleeved engine, and if it was bored into the old sleeves it's junk!

Wolfman, here's another thread with conflicting information regarding sleeves.
https://www.orangetractortalks.com/forums/showthread.php?t=10494

This thread makes it sound like the 0.5 re-bore is an option, if not preferred, to pressing in new sleeves... Just sharing what I found.

 

[Jim Dandy]

You can bore many of Kubota engines to accept oversized Pistons. Kubota and others offer oversize Pistons. Done properly you can save a fair amount of money on a rebuild.
James